Metal-Driven Biochemical and Physiological Stress in Fish Inhabiting an Urban Coastal Lagoon: Evidence from an...

Urban coastal lagoons are heavily impacted by untreated sewage, industrial effluents and diffuse pollution, heightening ecotoxicological risks. Herein, Nile tilapia (Oreochromis niloticus) was employed as a sentinel species concerning metal exposure at the Jacarepaguá Lagoon Complex (JLC), a critical case of ecological degradation under intense anthropogenic pressure in Rio de Janeiro, Southeastern Brazil. Samplings were conducted between 2022 and 2023 during the dry (autumn-winter) and rainy (spring-summer) seasons. Organosomatic indices and total (muscle) and subcellular (liver and muscle) metal levels were determined. Antioxidant system alterations were evaluated through superoxide dismutase (SOD), glutathione-S-transferase (GST), reduced glutathione (GSH), total antioxidant capacity (TAC) and metallothionein (MT) assessments. Lipid peroxidation (LPO) and protein carbonylation (PTC) levels were also determined as oxidative effect markers, while vitellogenin (VTG) was used as an estrogenic effect indicator. Arsenic (0.018-0.033 mg L⁻¹), Mn (0.041-0.050 mg L⁻¹), Rb (0.019-0.023 mg L⁻¹), and V (0.008-0.010 mg L⁻¹) were detected in water samples in both sampling seasons; while Fe was detected only in the dry season (0.023 ± 0.03 mg L⁻¹). Subcellular As, Co, Cu, Fe, Mn, Ni, Pb, Rb, Ti, V, and Zn were quantified in both liver and muscle, albeit with no significant differences between seasons or sexes. Seasonal variations were noted for male VTG, although not statistically significant, with attenuation of sexual VTG differences from the dry (M/F = 0.67) to the rainy season (M/F = 1.20). The multibiomarker approach applied to wild tilapia under diffuse urban pollution indicates mild sublethal effects while highlighting the need for expanded, integrated monitoring of additional endocrine and oxidative biomarkers. Although centered on a specific lagoon complex system, these mechanisms recur in urban lagoons worldwide, indicating the need for consumption-risk evaluations and actionable remediation/management frameworks.